PDA

View Full Version : plowing in.



garyfirth - n/a
14-Feb-09, 07:33 AM
I have a flying fish marlin,that i have used for one season

in that time have learned loads met some nice people.I have seen loads of different craft in the flesh and on the web.

I never for one moment thought

that i would get addicted to hovercrafting.

I am contantly messing with the fish sorting out problems or potential problems fitting extras to make life better for me.

But i have a problem with plowing in.

I hear people say it has happenned to them a couple of times,but it happens to me everytime i go out.I dont drive at full throttle

everywhere and it has the smaller briggs 22hp???I have had a baptism of fire with plowin the first being on the training day cruise on the lune (brown trouser moment),`i noticed the craft behaving strange and let the power off very gently then bam!Five front segs flappin about,the poor thing looked like it had been kicked in the teeth.I have had one other experince as severe on the humber last time out (see cruise on the humber thread),however everthing stayed together that time and i got a jolt through my arms by bracing myself for impact.

I have read that scat do a plow resistant bag for there craft does anyone have any ideas on how to stop it or recover without plowing in.

I have spoke to bryan and he mentioned a flap underneath the craft but i fear i would damage the flap.Ihave started to make the flap but i am open to ideas.

Cheers gaz

Irish Falcon - n/a
14-Feb-09, 08:40 PM
Here's (http://books.google.ie/books?id=T3hPcUQdurwC&pg=PA173&lpg=PA173&dq=hovercraft+plough+in&source=bl&ots=OdUL9muXM9&sig=pJaoSPjYLfXPUXwa0e93zFw4Dto&hl=en&ei=iDaXSbb-DeS1jAeXi4zkAQ&sa=X&oi=book_result&resnum=5&ct=result#PPA179,M1) some of the theory involved. Philip

Don83000 - n/a
15-Feb-09, 12:07 AM
I have a flying fish marlin,that i have used for one season

in that time have learned loads met some nice people.I have seen loads of different craft in the flesh and on the web.

I never for one moment thought

that i would get addicted to hovercrafting.

I am contantly messing with the fish sorting out problems or potential problems fitting extras to make life better for me.

But i have a problem with plowing in.

I hear people say it has happenned to them a couple of times,but it happens to me everytime i go out.

Cheers gaz






So you guys out there with Flying Fish just how big a problem is this . Is this more prevalent with the lower hp heavier B&S and the Marlin or is it a problem across the Flying Fish range

GavinParson - n/a
15-Feb-09, 08:51 AM
Plough in can happen to any craft especially downwind as Alan Bliaults book explains.

Unless you can supply extra air to the front skirt or partition it to maintain the cushion pressure against the external ram air at speed then it will plough in.

The weight of a B&S at the rear of a craft is irrelevant and if anything helps the situation by creating a higher skirt pressure at the rear thus moving more air to the front of the craft.

Plough in can be controlled by driver awareness and corectly trimming the craft depending on the prevailing wind conditions.

Craft with a lift fan with separate air ducting to the front skirt can minimize the problem. Any integrated craft is more likely to plough in as the air has further to travel from the fan and loses velocity and pressure on the way.

But I'm sure you already knew that.

Kipmac - n/a
15-Feb-09, 09:32 AM
Gaz,

From my own experience I am aware that you can plough in an integrated craft in particular by trying too hard NOT to plough in.

By sitting too far back in the craft you can arrive at a situation where the rear chip bags (if fitted) can grab the water at the inner attachment point and in doing so it can result in rapid loss of speed and the nose slamming down.

I must hold the record for Kestrel plough ins at Stanford Hall until I began to trust the craft and trim it better.

If and when you feel one coming on try chucking the craft sideways and when travelling down wind you should constantly shift the craft angle gently left and right.



If you can, go out with a similar craft and check your trim against the other craft or have the other driver check you out.



Hope this helps.

Kip



N.B Is it Plough or Plow??

garyfirth - n/a
15-Feb-09, 02:02 PM
Please remember i have low hours on hovercraft.

inexperience could be a major part of the problem.everytime a plowin has happened i have been in a straight line for a long period of time.

Please dont be put off fish because of this i love mine a would not be without it,it is reliable and fun.

I JUST NEED ADVICE TO HELP SORT IT/MY PROBLEM.

Rear skirt mod need testing (sealed half way up)

Nauti Buoy - n/a
15-Feb-09, 03:33 PM
I should of course be pointed out that Don Underwood has an issue with me and takes every opportunity he can to try and damage the reputation of Flying Fish hovers, with well constrcuted posts such as the one above. If he were to buy a Flying Fish craft (yeah-right.... http://hovercraft.org.uk/images/icons/smiley_icons/icon_rolleyes.gif) he'd need to buy a used one - there's no way we'd sell him one.



Gazza - by all means buzz me on 0845 07 11 178 for a chat.



Russ

garyfirth - n/a
15-Feb-09, 04:10 PM
I can safely say i would love to buy a new fish if i had the money.

You must remember my fish is an exracer, and it has a few years under its belt.I am sure they have made many improvements since mine was built.

saying that i still think that my fish was good value for money and smiles per it cant be beat

Buy one and see for yourself,

i am learning alot about this sport and loving it,

would love to race but i am sure as with most motor sport money wins

bryan - n/a
15-Feb-09, 04:20 PM
Don lighten up...! The fish boys were good enough to lend me a craft as a problem cropt up with my own. I spent around 3 hrs on and off mud banks on a tour of the Sheppy area. Yea the nose is a bit twitchy down wind but it was never a problem. I think i used about an egg cup of fuel all day....... made a nice change!!! An all round easy to use craft with no excess of spanners.

Don83000 - n/a
15-Feb-09, 05:16 PM
Bryan why tell me to lighten up I had only asked a simple question and recieved a good answer from Gavin with him saying that (reading between the lines) the SEV is the way to go for safety as he points out that a partitioned front skirt is the best way to avoid ploughing in.

Quite why Russ Pullen can't accept what Gavin is saying without throwing his toys out of the pram is beyond me maybe he should lighten up !!!. I would just like to thank Gazza for pointing out the problem in the first place and even yourself Bryam say Quote "Yea the nose is a bit twitchy down wind" so to make that comment that must be a warning in its own right.

john stead - n/a
15-Feb-09, 05:31 PM
Quote (would love to race but I am sure as with most motor sport money wins)

Do not be put of racing it’s not only the money that wins although it helps. It does not matter how much money you throw into it if 1 you can’t drive, 2 you don’t learn form your mistakes, there a quite a few drivers out there who do not throw loads of money at the sport myself included and remember the old saying IT’S NOT THE WINNING IT’S THE TAKING PART THAT COUNTS (although standing on the podium is a good feeling finishing a race in one piece and not having damaged any one else’s machine doing it is good enough for most people)

GavinParson - n/a
15-Feb-09, 06:00 PM
a good answer from Gavin with him saying that (reading between the lines) the SEV is the way to go for safety as he points out that a partitioned front skirt is the best way to avoid ploughing in.






I meant a partitioned cushion area, not front skirt. i.e. such as many racers are now using with a divider to maintain the cushion in the front.

Sevs can still plough in as can any craft in certain conditions.



I'm waiting to test Hovpods claim that they don't plough in.

jar2 - n/a
15-Feb-09, 07:43 PM
<table border="0" align="center" width="90%" cellpadding="3" cellspacing="1"><tr><td class="SmallText">Don83000 wrote on Sun, 15 February 2009 18&#58;16</td></tr><tr><td class="quote">
a good answer from Gavin with him saying that (reading between the lines) the SEV is the way to go for safety as he points out that a partitioned front skirt is the best way to avoid ploughing in.






I meant a partitioned cushion area, not front skirt. i.e. such as many racers are now using with a divider to maintain the cushion in the front.

Sevs can still plough in as can any craft in certain conditions.



I'm waiting to test Hovpods claim that they don't plough in.
</td></tr></table>



I don't think Gav was intending anything "between the lines" Don.



Plough in can happen with ANY hovercraft - the difference between craft is in the end result of the plough in. On some craft (as Gazza has found out) the deceleration can be very severe, on others it's a mild braking or slowing down. Large commercial craft "fixed" the plough in problem 30 years ago (ever wondered why large craft have a big bulbous front skirt?).



Sevs have a partitioned cushion and not a partitioned skirt. The cushion is divided by a partition skirt roughly 75% rear/25% front with the forward cushion compartment operating at a slightly lower pressure than the main cushion. Although normally very stable, they can still plough-in if you get the wrong combination of wave depth and frequency. However, due to the raised boat-like underhull the event is pretty insignificant - the craft just slows down a bit, recovers and then carries on.



Gazza, it may be worth contacting Ralph DuBose in the US - he developed an anti-plow modification for a Scat he had that apparently made the craft virtually plough-in-prof (Scat are/were notorious for unpredictable plough-in).



I would be very surprised if HovPods don't plough-in, they appear to have attempted an underhull step as an anti-plough solution (as used in hydroplanes - and UH hovercraft for the last 30 years http://hovercraft.org.uk/images/icons/smiley_icons/icon_biggrin.gif ) to prevent water becoming attached to the hull (water attachment is the cause of the sudden stop during a plough). Unfortunately, they rounded off the sharp step edge which has probably removed any effect it may have had.

Vortex - n/a
15-Feb-09, 07:59 PM
Hi there,



Keith adding his bit, somewhere on the north sea going to Denmark.....no its not rough.....yet..





Despite what you read on various websites...all craft will plough in at some point..if yours doesn't you aren't going fast enough!!!



Skirt pressure and skirt design determines when plough in will happen it could be at 30mph or 80mph......but it will happen!!!



and no bag skirts don't stop it they mearly change when and how it happens



Keith

Keith Oakley - n/a
15-Feb-09, 09:30 PM
I agree with all the above - all craft will do it sometime. But you might delay it by using a variable splitter plate. If you're trying to go along at 'half power' in an integrated craft the air feed to the front will be reduced and eventually a plough in will occur. Fitting a variable splitter, common on integrated racing craft, allows you to increase the ratio of air used for lift. Not easy on a marlin though because of the way the fan frame aligns with the splitter.

Ian Brooks - n/a
15-Feb-09, 09:41 PM
A bit of background...



What is plough-in?



Plough in is a phenomenon that occurs when the nose of a hovercraft suddenly drops. Often associated with sudden deceleration, uncontrolled swerving and in extreme cases the occupants can be thrown from the craft which might even roll over. It caused the death of several people in 1972 when an SRN6 overturned, so has to be taken seriously.



What causes plough-in?



Most people agree that plough-in follows the following sequence:



1 - A hovercraft flying in straight and level flight before the event, with the bow skirt clear of the water



2 - The bow drops slightly and the tip of the bow skirt touches the water causing hydrodynamic drag on the skirt - the water "tugs" at the skirt. Experienced pilots can feel this occurring at this stage and take avoiding action, but novices don't usually notice anything wrong.



3 - The bow skirt begins to tuck under due to the tugging of the water, causing the nose to drop. As the skirt tucks under, it pulls back under the craft causing the center of pressure to move backwards.



4 - The nose drops further, increasing the hydrodynamic tugging, and the skirt tucks under completely. Once this stage is reached, a full-on plough is inevitable.



5 - The bow drops sharply until some hard structure hits the water. What happens next depends on the shape of the bit of hull that touches down. It might "dig in" causing the craft to stop like it hit a wall, or to "plane" over the water and decelerate more reasonably.



6 - The final stage is sudden severe uncontrolled deceleration if the structure digs in, or sudden but survivable deceleration.



When does this happen?



Plough-in happens when the hydrodynamic forces can overcome the skirt tension & make them tuck-under - that is, at high speeds.



It's worse when flying downwind for reasons that don't seem absolutely clear, with integrated craft the lift air might be reduced which makes it worse, and the aft-wind probably causes a more nose-down trim which helps to initiate the event, plus the craft may well be going faster than usual.



It only happens on water.



How can you stop it?



If you have a craft that tends to plough, you learn to spot the "tugging" stage and react by increasing lift and trimming the nose up by moving weight backwards or altering the elevator.





How do you prevent it by design?



Plough-in can be designed out at step 3 or 4, and the end effect can be controlled at 5.



At step 3:



- Design the skirt so that it cannot tuck-under (Sevtec curtain).

- Design so that the bow dropping forces the skirt to move forwards thus preventing further drop (Wouters "bulbous" bow skirt).

- Increase the skirt tension (pressure) so that it overcomes the water drag (pressure segs)



At step 4:



Partition the cushion and feed the front partitition from a pressure higher than it "normal" pressure. As the bow drops, the skirt seals and allows the partition pressure to rise. This opposes the downward forces and lifts the bow back out of the plough-in. This can be done by various means:

- Sevtec style "divider curtain"

- Inflatable tubes

- Rubber flexible dividers (Bryan's design)

The typical segment skirt craft with air delivered via a plenum seems to be suited to either of these methods, and Bryan showed that the divider can be quite a loose fit under the craft.



At step 5:



Make sure the part of the craft that touches the water first does so at a shallow angle - about 10-15 degrees seems about right.



Sideways plough-in

All the above applies to forward travel. When operating sideways, the same can thing can happen. With small craft, it is effectively prevented by the pilot altering sideways trim. With a large craft, it has to be prevented by keeping speed down for large angles of yaw.



Cheers

Ian

garyfirth - n/a
16-Feb-09, 06:27 PM
side ways plowin

nobody told me of this

oh my god the craft has more ways of trying to kill me

have i missed something.

do i need a a pocket built in the craft to store my last will and testament.

do i need to up my life insurance?

is it too late to start knitting,

sod this for a game of soldiers i am going morris dancing.

Keith Oakley - n/a
16-Feb-09, 06:31 PM
Of course it is also possible to do a backwards plough in but it does take more skill. You need to do a 180 degree twistle turn quick enough to be travelling over hump backwards then do something panicky like shutting the throttle.....

Ian Brooks - n/a
16-Feb-09, 06:32 PM
you'll be alright.... just lean into the corner and all will be well!



Ian

garyfirth - n/a
16-Feb-09, 06:50 PM
backwards ahhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh

team black - n/a
16-Feb-09, 07:10 PM
side ways plowin

nobody told me of this

oh my god the craft has more ways of trying to kill me

have i missed something.

do i need a a pocket built in the craft to store my last will and testament.

do i need to up my life insurance?

is it too late to start knitting,

sod this for a game of soldiers i am going morris dancing.






http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=14 (http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1478668) 78668

Nauti Buoy - n/a
16-Feb-09, 07:25 PM
<table border="0" align="center" width="90%" cellpadding="3" cellspacing="1"><tr><td class="SmallText">gazza wrote on Mon, 16 February 2009 19&#58;27</td></tr><tr><td class="quote">
side ways plowin

nobody told me of this

oh my god the craft has more ways of trying to kill me

have i missed something.

do i need a a pocket built in the craft to store my last will and testament.

do i need to up my life insurance?

is it too late to start knitting,

sod this for a game of soldiers i am going morris dancing.






http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=14 (www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1478668) 78668
</td></tr></table>





i would have thought that suicide is a bigger threat - i mean imagine waking up one morning and suddenly realising......



'i'm a Morris Dancer' or 'I'm a Norfolk Turkey'



I imagine suicide would be the only realistic option.

garyfirth - n/a
16-Feb-09, 07:26 PM
ok so morris dancing is out.

what about wrapping myself in cotton wool and staying in bed.

being fed through a rubber tude(no sharpe edges)

ha that will do nicely.

GaryH - n/a
16-Feb-09, 08:40 PM
side ways plow in http://hovercraft.org.uk/images/icons/smiley_icons/icon_eek.gif as i discovered the other day is scary stuff. http://hovercraft.org.uk/images/icons/smiley_icons/icon_sad.gif frightened the hell out of me, my passenger nearly went over the side. couldent stop laughing for ages http://hovercraft.org.uk/images/icons/smiley_icons/icon_twisted.gif

kevthehover - n/a
16-Feb-09, 09:31 PM
<font color="darkblue">So you are a morris dancer now then, Nauti Bouy? as you said

'i'm a Morris Dancer'



I would rather have a Norfolk Bird than a Merry Morris Dancer from Kent any time................Lol http://hovercraft.org.uk/images/icons/smiley_icons/icon_lol.gif http://hovercraft.org.uk/images/icons/smiley_icons/icon_lol.gif http://hovercraft.org.uk/images/icons/smiley_icons/icon_lol.gif



Kindest regards

Kev[/COLOR]

Happy Snapper - n/a
17-Feb-09, 08:46 AM
are you gonna be racing??

I will definatly keep my camera on you if you going to be doing stunts!! http://hovercraft.org.uk/images/icons/smiley_icons/icon_lol.gif

hovmart - n/a
17-Feb-09, 09:31 AM
the advantage of flipping the craft of the straight forward line is that as you feel it start to plough you can give it full power increasing the air flow with out in creasing the speed, and its lack of airflow with to much speed that causes the problem in the first place

Burtythepilot - n/a
18-Feb-09, 02:01 AM
Since everyones commented on ploughing in, if the definition's described as "A phenomenon that occurs when the nose of a hovercraft suddenly drops." then Gazza, you need a BBV. They are the most resilient to ploughing in.



Owned mine for 2 years, been on most events, can take it where most other hovercraft don't seem to want to go and apparently then, it has never ploughed or plowed in, not once.



I tried a flat out run when it was new to test this, the front skirt collapsed at 45 mph on the GPS I was holding in my free hand, the BBV design of the hull turns it into a speed boat so that it just rides nose up, the tail will eventually sink in first.



Most stupid thing I did was near flat out, knocked off the lift motor lanyard. So, while it was apparently plowing in, with one hand I could put the lanyard back on and with the other press the start button and set off again without loosing a place, it didn't spin out and no I didn't loose control, because you can keep the thrust still on.



You can abuse the BBV's knowing reassuringly that they are not going to bite, forward, sidewards, backwards. Next time we are all on a cruise, come and have a go, I'll buy the beer all night to the first person who can make my BBV plough in. 5 a go...

bryan - n/a
18-Feb-09, 04:34 PM
Your BBV must be different to to the others i,ve been in and cruised with. So far your craft is the quietest and never ploughs in. Bill Baker must be very proud that you have made his craft perfect!!!!!.

Still i would like the opportunity to drink all your beer and take your money.....Cheers Colin http://hovercraft.org.uk/images/icons/smiley_icons/icon_biggrin.gif http://hovercraft.org.uk/images/icons/smiley_icons/icon_biggrin.gif http://hovercraft.org.uk/images/icons/smiley_icons/icon_biggrin.gif

hovmart - n/a
18-Feb-09, 04:47 PM
we just need a windy day it will pay for the beer http://hovercraft.org.uk/images/icons/smiley_icons/icon_redface.gif

jar2 - n/a
18-Feb-09, 05:59 PM
Gazza, you need a BBV. They are the most resilient to ploughing in.




Maybe there is a misunderstanding here but BBV's are no more immune to the laws of physics than any other hovercraft.



Watch this video (www.youtube.com/watch?v=gO9aH82B6HI&feature=channel) around 6:30 and you will see what looks suspiciously like a BBV ploughing in (I could be mistaken though http://hovercraft.org.uk/images/icons/smiley_icons/icon_biggrin.gif ).



I'm not knocking BBV craft - they are well made and do the job nicely but, as verified by other owners on this thread, every other craft design ploughs in with various degrees of severity - BBV's are no different.

john stead - n/a
18-Feb-09, 09:59 PM
Oh it was only a matter of time before this one reared its head and you just know this is my favourite subject (time to light the blue touch paper http://hovercraft.org.uk/images/icons/smiley_icons/icon_twisted.gif ) B.B.V ploughing and spinning out of control unheard off B.B.V staying under control on the rare occasion they do plough. ALWAYS. lets see how many have I ploughed mine in the last four years I can count them on one hand and before anyone says it’s because it’s not being driven hard enough then think again. I ploughed once at claydon house drove over half the length of the lake flat out with water coming over the nose still under control. Last year the comment was made after one race (I saw you plough in that race) to me for someone to comment about my craft ploughing it must really be a very rare sight indeed. http://hovercraft.org.uk/images/icons/smiley_icons/icon_biggrin.gif http://hovercraft.org.uk/images/icons/smiley_icons/icon_biggrin.gif

Paul Fitz - n/a
18-Feb-09, 11:50 PM
<table border="0" align="center" width="90%" cellpadding="3" cellspacing="1"><tr><td class="SmallText">Quote:</td></tr><tr><td class="quote">
the BBV design of the hull turns it into a speed boat so that it just rides nose up
</td></tr></table>



I remember Kristie Scales at Lydd closing the throttle from flat out.... it didn't boat! She did.... about 5 metres in front of the craft. http://hovercraft.org.uk/images/icons/smiley_icons/icon_surprised.gif)



As hovmart said, too much speed and lack of air....



Paul

hover t - n/a
19-Feb-09, 12:36 AM
Thats a deep hole you have managed to dig for yourself this time Burtyhttp://myweb.tiscali.co.uk/dirtbox/pics/muttley.gif

some of the members could cost you a fortune to keep going with beer all night

Trev http://www.clicksmilies.com/s0105/mittelgrosse/medium-smiley-064.gif

hovmart - n/a
19-Feb-09, 08:11 AM
mind you we all know HOVPODS dont plough in http://hovercraft.org.uk/images/icons/smiley_icons/icon_rolleyes.gif

hoverchaps - n/a
24-Feb-09, 09:22 PM
Cos hov pods have chip bags at the front so don't hover but plow along , oh and are the HEAVIEST things ever so skirt pressure about 50psi.

hovmart - n/a
25-Feb-09, 08:57 AM
more like BOATPODS then, you have to be hovering before you can plough in http://hovercraft.org.uk/images/icons/smiley_icons/icon_biggrin.gif

team black - n/a
26-Feb-09, 05:56 PM
An interesting time to pose the question: How many people have actually driven hov-pods? I have

Irish Falcon - n/a
26-Feb-09, 06:23 PM
I've sat in one does that count? Philip

jon_curtis - n/a
26-Feb-09, 06:56 PM
i have had a chance to get a very good look over one, close up! there is nothing specifically special about the design to limit plough, they do have a secondary plane on the front planning surface that cuts under, assuming to help lift out of a plough.

they do also have high pressure segements on the front of sorts! not exactly chip bags, but sealed on the rise to provide a firmer front segment (funny same as on my ally craft, which is less likely to plough in with them on)



i wouldnt say they are plough proof, they most certainly do hover well, they are not that heavy, they just look substantial.

nothing wrong with a hoverpod in my opinion except the very very high price!

hoverchaps - n/a
26-Feb-09, 08:41 PM
I have been under the front and cant see a secondary plaining surface. can you describe what i am looking for? It may have fallen off .

if it takes 4 large blokes to lift it (not carry lust lift) is not heavy i suppose.

Has anyone got the 45mph as advertised?

hoverchaps - n/a
27-Feb-09, 09:11 AM
Can someone describe the anti polw in device that exists as i think it may have fallen off as nothing clever exists.

No not heavy only takes 4 blokes to lift it ( not carry needs 2 more). Sealed bags at front stops air lubrication so plow along. Has anyone done the advertised 45 mph please.

sixpackpert - n/a
27-Feb-09, 11:22 AM
Has anyone done the advertised 45 mph please.




On or off the trailer? http://hovercraft.org.uk/images/icons/smiley_icons/icon_lol.gif

jon_curtis - n/a
27-Feb-09, 12:17 PM
the front planning surface comes down at the same angle as the sides, then cuts under to a shallower angle, giving you effectively two planning surfaces, like the underside of a sevtec in a way. this would not fall off!



the hovpod i have seen did not have totally sealed front segments they were still open at the bottom with a fist sized hole, but like a chip bag, sealed upto the planning surface?



does this hovpod you have plough in bad then?



does it have a 503 engine with the zorst behind the engine under the cover? this can cook the rear cylinder, or it did on the pod i saw!